This invention relates to electrophotographic printing machines. Specifically, this invention relates to electrophotographic printing machines having seamed intermediate transfer belts. These belts are made from flat sheets formed as a continuous belt using a puzzle cut joint.
Electrophotographic printing is a well-known and commonly used method of copying or printing documents. Electrophotographic printing is performed by exposing a light image representation of a desired document onto a substantially uniformly charged photoreceptor. In response to that light image the photoreceptor discharges, creating an electrostatic latent image of the desired document on the photoreceptor""s surface. Toner is then deposited onto that latent image, forming a toner image. The toner image is then transferred from the photoreceptor onto a receiving substrate such as a sheet of paper. The transferred toner image is then fused with the substrate, usually using heat and/or pressure. The surface of the photoreceptor is then cleaned of residual developing material and recharged in preparation for the production of another image.
The foregoing generally describes black and white electrophotographic printing machines. Electrophotographic printing can also produce color images by repeating the above process for each color of toner that is used to make the color image. For example, the photoreceptive surface may be exposed to a light image that represents a first color, say black. The resultant electrostatic latent image can then be developed with black toner particles to produce a black toner layer that is subsequently transferred onto a receiving substrate. The process can then be repeated for a second color, say yellow, then for a third color, say magenta, and finally for a fourth color, say cyan. When the toner layers are placed in superimposed registration the desired composite color toner image is formed and fused on the receiving substrate.
The color printing process described above superimposes the color toner layers directly onto a substrate. Other electrophotographic printing systems use intermediate transfer belts. In such systems successive toner layers are electrostatically transferred in superimposed registration from the photoreceptor onto an intermediate transfer belt. Only after the composite toner image is formed on the intermediate transfer belt is that image transferred and fused onto the substrate. Indeed, some electrophotographic printing systems use multiple intermediate transfer belts, transferring toner to and from the belts as required to fulfill the requirements of the machine""s overall architecture.
In operation, an intermediate transfer belt is brought into contact with a toner image-bearing member such as a photoreceptor belt. In the contact zone an electrostatic field generating device such as a corotron, a bias transfer roller, a bias blade, or the like creates electrostatic fields that transfer toner onto the intermediate transfer belt. Subsequently, the intermediate transfer belt is brought into contact with a receiver. A similar electrostatic field generating device then transfers toner from the intermediate transfer belt to the receiver. Depending on the system, a receiver can be another intermediate transfer member or a substrate onto which the toner will eventually be fixed. In either case the control of the electrostatic fields in and near the transfer zone is a significant factor in toner transfer.
Intermediate transfer belts often take the form of seamed belts fabricated by fastening two ends of a web material together, such as by welding, sewing, wiring, stapling, or gluing. While seamless intermediate transfer belts are possible, they require manufacturing processes that make them much more expensive than similar seamed intermediate transfer belts. This is particularly true when the intermediate transfer belt is long. While seamed intermediate transfer belts are relatively low in cost, the seam introduces a discontinuity that interferes with the electrical, thermal, and mechanical properties of the belt. While it is possible to synchronize a printer""s operation with the motion of the intermediate transfer belt such that toner is not electrostatically transferred onto the seam, such synchronization adds to the printer""s expense and complexity, resulting in loss of productivity. Additionally, since high speed electrophotographic printers typically produce images on paper sheets that are cut from a paper xe2x80x9cweb,xe2x80x9d if the seam is avoided the resulting unused portion of the paper web must be cut-out, producing waste. Furthermore, even with synchronization the mechanical problems related to the discontinuity, such as excessive cleaner wear and mechanical vibrations, still exist.
Acceptable intermediate transfer belts require sufficient seam strength to achieve a desired operating life. While the desired operating life depends on the specific application, typically it will be at least 100,000 operating cycles, and more preferably 1,000,000 cycles. Considering that a seamed intermediate transfer belt suffers mechanical stresses from belt tension, traveling over rollers, moving through transfer nips, and passing through cleaning systems, achieving such a long operating life is not trivial. Thus the conflicting constraints of long life and limited topographical size at the seam places a premium on adhesive strength and good seam construction.
A prior art xe2x80x9cpuzzle cutxe2x80x9d approach to seamed intermediate transfer belts significantly reduces mechanical problems by producing an improved mechanical seam.
U.S. Pat. No. 5,514,436, issued May 7, 1996, entitled, xe2x80x9cPuzzle Cut Seamed Belt;xe2x80x9d U.S. Pat. No. 5,554,193, entitled xe2x80x9cEndless Seamed Belt with Low Thickness Differential Between the Seam and the Rest of the Belt;xe2x80x9d and U.S. Pat. No. 5,487,707, issued Jan. 30, 1996, entitled xe2x80x9cPuzzle Cut Seamed Belt With Bonding Between Adjacent Surface By UV Cured Adhesivexe2x80x9d teach the puzzle cut approach. While puzzle cuts reduce mechanical problems there remains other difficulties with transferring toner onto and off of a seam of a seamed intermediate transfer belt.
The process of cutting the petals in the belt material to form the puzzle cut joints presents a challenge to those attempting full automation. There is a continuous need through out the cutting process to maintain close tolerances. These tolerances require high precision in the handling of the belt material and the continuous registration of the belt material with the cutting and handling apparatus. In addition this must be accomplished while maintaining the belt material free of contamination.
It is a purpose of the system of this application to provide an automated system and process for cutting the belt material in preparation for joining the ends of the belt material into a continuous belt. It is another purpose of this system to accomplish this while minimizing contamination and damage. It is another purpose of the system of this application to maintain accurate positioning of the belt continuously through the cutting process.
The system of this application provides a means of fabricating a flat sheet of belt material into a blank for use in forming a continuous belt. Such belts are used in various functions within a printing system, as discussed in the above background section. A two stage cutting system is constructed having a first work station which is designed to cut the belt blank to predetermined dimensions and a second station which is designed to accurately punch the petal configuration of the puzzle cut in each end of the blank.
The first station is comprised of a cutting blade mounted on an x-y support for computer controlled motion over a cutting table. The puzzle cut station is constructed having a left and right die set mounted over a punch table on which the blank is clamped for performing a first punch operation by one of the die sets on one end of the blank and then moved a predetermined distance to the other punch/die set for a repeat punch operation on the other end. Within the punch station there are also left and right optical position sensors which align and register the blank with the die set prior to each die cut. A pick and place transport mechanism picks up the blank from the precision cutter station and moves it to one of the die sets of the punch station. Vacuum pickup bars are used to engage the blank and secure it in position and maintain the blank in a taut condition.
As a first step of the method of this application, a flat sheet of belt material is smoothed out and secured by vacuum on a cutting table in registration with a precision cutter. The sheet of belt material is registered in place on the cutting table and held by a vacuum. The material is cut into a blank to predetermined dimensions, with its width and rectangular shape being within close tolerances. The length is cut oversized to facilitate processing in the punch station.
After the cutting operation, the blank of belt material is engaged by the pick and place mechanism. The pick and place mechanism is moved over the blank with a slight clearance. Simultaneously the vacuum of the vacuum bars is applied while the vacuum of the cutting table is reversed. This insures a reliable and accurate release of the blank from the cutting table.
The blank is then removed from the table and placed in the punch station. Again to insure proper positioning and registration in the punch station, the pick and place mechanism maintains the blank in a flattened and taut condition as it is introduced into the punch station.
The blank is positioned on the work platform of the punch station in registration with one end of the punch by means of an optical monitor, which senses and registers a lengthwise edge of the blank. When one end is registered with the respective punch die set, the blank is clamped and punched. After one end is punched with the puzzle cut petals, the belt is released from the clamp and shifted a predetermined distance to the other punch die set by the pick and place mechanism to cut the mating petals. At each position, the location of the blank is monitored by an optical system to insure continuous alignment of the blank in the punch station. Left and right optical sensors insure the registration of a lengthwise edge with the die set. Limited x-y motion is provided by the vacuum bar supports to move the blank from one punch set to the other.